1. Field
The present application relates to voice telephony, and more particularly to control and status signaling to and from mobile devices over voice channels, such as in third party call control.
2Related Art
Voice telephony remains a major application of interest for business and personal use. In an example corporate setting, a telephony installation at a site can have a large number of users connected to a Private Branch Exchange (PBX) server, which can interface those users to a smaller number of outside lines (e.g., an E1 or T1 line) (a PBX can be implemented using a server with telephony cards for example). A PBX can interface with other servers and systems, such as one or more application servers that can provide enhanced services to devices connected to the PBX, such as mobile devices. For example, a PBX can interface with an application server over an IP connection, using SIP signaling. Services provided by an application server can include voice mail, single number reachability, call forwarding, park, and conferencing, for example. PBX systems also can communicate with each other over trunk lines, and packet networks, depending on implementation.
A PBX can perform services for a voice call, based on direction from an application server. For example, a PBX can initiate an outgoing call to a number specified by an application server using SIP signaling to the PBX, and bridge a mobile device that requested such call. Continuing this example, it would be desirable to provide status information to the requesting mobile device. Such status information would include information such as whether the remote party phone has started to ring or not. Still further, initiating commands, such as call transfer, and sending status information during progress of such commands also desirably is available. In absence of a data channel that can be maintained concurrently with a voice channel, this information can be communicated using DTMF tones. However, a number of considerations desirably should be addressed if using DTMF tones for such purposes, and aspects herein relate to alleviating some of these concerns.